Present day communication networks for tactical situations typically include directional communication links extending from individual military sites, which will be called remote stations, and retransmitting stations, which will be called central stations. Further directional links, called trunk groups, exist as between each pair of central stations within communication reach of each other. A representative of such system is shown in U.S. Pat. No. 4,125,808 which issued to L. H. Graham on Nov. 14, 1978. As will be seen in FIGS. 1 and 2 of this patent, remote stations are denominated BCU (basic communication unit) and the central stations are denominated RTU (retransmission unit). Directional links are found in the system of the '808 patent as between each BCU and its assigned RTU and other directional links (trunk groups 10-24) exist among the RTUs. Each of links 10-24 is comprised of a multi-channel radio link or trunk group, each trunk being at a unique frequency. Each central station includes a switching center, such as the customary AN/TTC-39 Line Circuit Switch, which functions to assign trunks individually to telephone conversations between the participating BCUs.
In operation of the system of '808 patent, the communication path between BCU's assigned to different RTU's is established by an inquiry transmission by the assigned RTU to all RTU's to which it is directionally connected as to whether the desired BCU is assigned to such RTU's. If the answer to the inquiry is affirmative, the path is established. If the answer is negative, each RTU inquired of retransmits the inquiry to those RTU's with which they are in directional communication.
In the '808 system, some effort is directed at monitoring transmission quality. As is shown in FIG. 3(b) of the '808 patent, its system includes a signal-to-noise detector which, in the course of channel selection, advises a channel selector of the signal-to-noise ratio on a channel being considered for use. Should the ratio be unacceptable, the selector advances to a different channel for like signal-to-noise inquiry.
While one finds in systems such as the '808 patent system an adaptiveness to changing radio connectivity conditions, such as the loss of a retransmission unit or a poor transmission quality condition on a given channel, these benefits are obtained with a system architecture which undesirably is highly frequency involved and depends vastly upon directional communication and trunk assignment on a central-to-central basis. Thus, each RTU broadcasts in multi-frequency transmissions and requires plural directional antennas. The probabilities are accordingly heightened for interference and setup and redemployment times can be excessive for mobile combat situations.